


Shaping Up

by Grotesque (Grotesque_Flower)



Category: Gravity Falls
Genre: Anyway back to relevant tags, Is this smut idfk, M/M, Rimming, Shape Rimming, Shape!Dipper, Tentacles, This is fucking weird okay, Triangle!Bill Cipher, if i say pine tree people may think dippers a literal tree, oh god what if like human AU as kids bill, triangle!Bill, was one of those weird kids who would marry trees
Language: English
Status: Completed
Published: 2016-06-27
Updated: 2016-06-27
Packaged: 2018-07-18 13:10:01
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,938
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7316401
Author URL: https://archiveofourown.org/users/Grotesque_Flower/pseuds/Grotesque
Summary: <blockquote class="userstuff">
              <p>Bill always switches into his human form for Dipper during intimacy, but what if Dipper turned for him?</p>
            </blockquote>





	Shaping Up

**Author's Note:**

> This is fucked up

Oh how Dipper was giddy. But then again he always was giddy when he had the house to himself. Because when his sister and two great uncles were away doing whatever it was they did when he wasn’t accompanying them, it mean that he could spent some quality alone time with Bill. And ten out of eleven times that ‘quality alone time’ meant one thing. And we all know what it was.

Dipper knew Bill was around, he had come to be able to sense his lingering presence even when he couldn’t visibly see him. He was hanging around all day with the occasional drifting away before coming back. He didn’t say anything and Dipper was allowing him to actually step into his view whenever he was ready, but the boy was steadily growing impatient. He made his way to the spare bedroom that had become his own over the many summers he had stayed at the shack. The door creaked on its hinges when he opened and closed it behind him, he didn’t bother with locking it behind him. He simply took to taking off his clothing starting with his shirt. He did so slowly incase Bill was watching.

He pulled the simple band tee he wore that day over his head and shook his head to get his dark curls out of his face before tossing the shirt to the corner that had claimed its state as the laundry pile. Moving onto his shorts he was met with a small hand beating him to it. He let out a ‘huh’ when he looked down at his side to see that Bill, still in his angular triangle form, had rested his small hand at the hem of his shorts right where Dipper had planned to hook his thumb underneath. 

“Keep ‘em on, short stack,” Bill tried to speak playfully but there was something underlying in his voice that Dipper couldn’t exactly place but knew was there.

Dipper furrowed his brows but let his arms fall to his sides in rest, “You wanna do it yourself? Might be a little hard in your state- I mean! Duh, you have magic of course, never mind, forget I said that.”

Bill chuckled and floated his way up to his human’s shoulder and patted the bare sun freckled patch before he sighed, “Pine Tree, you know, I’m gonna cut to the chase here with you, okay?”

Dipper nodded and moved to look directly at the demon.

“You know, there’s a reason i didn’t know up earlier today, i’ve been thinking about tonight-”

“What about?” Dipper couldn’t help but feel a rise of panic set in his chest at the way the other was speaking.

“Hey, hey, calm down, yeesh, it’s nothing bad. Just thinking,” Bill leaned back a bit to cross his thin legs, “Sapling, I sure do a lot for you, sexually wise and not. And we haven’t done too much that cater to what I wanna do-”

“Bill, we’re always doing what you want. I let you do pet play despite the fact that you know i hate it!” the human of the two folded his arms over his bare chest defensively.

The demon rolled his eye, “I was experimenting… Geez, besides, you looked great. I mean that i change into whatever you want, whatever pleases you. I’m almost always human when we do these rendezvous, don’t get me wrong I love being your eye candy,” Bill leaned forwards and cupped the other’s chin with his hand, “I mean, my entire form is based on every little thing you look for in a male lover. But, what about you?”

Dipper couldn’t help but scowl, he had no idea where exactly the demon was getting at but it didn’t at all sound too good, “Are you saying that you find me unattractive? Because if that’s the case, so sorry i don’t appeal to you. I can’t just change my form to be whatever the hell you find physically attractive! Stuck with my ugly face an-”

“Oh my God, geez, Pine Tree okay listen i’ll cut to where i’m going at,” Bill sighed loudly and rolled his eye, “I’m always changing into human for you, well almost always, I appreciate that you’ll still fuck with me even in my natural form. But tonight, I wanna try something new!”

“What’s new…” Dipper grumbled to himself but Bill snapped his fingers in front of his nose.

“Hey! I wanna show you what it’s like from my side, when i’m in this form with you!”

The words didn’t truly register all the way with him. Dipper narrowing his mocha eyes at Bill as he tried to figure out what the hell he meant by it all. But the look in the demon’s eye was a smile and a playful one at that. Dipper was confused to the point of it being entirely obvious but Bill simply moved downwards to pull up his wrist to gesture for him to shake his hand. Dipper watched him, lifting his hand on his own up and watching the way Bill followed it up with it. 

“You’re not gonna possess me again, are you?” Dipper spoke wearily.

“Ugh, no! I haven’t done that in months! Something else is in mind, come on come on come!” If the demon had a tail he would surely be wagging it by now in anticipation. 

He took one last look at Bill before sighing inwardly to himself, taking hold of the small hand that was presented to him and shaking it. His eyes squeezed shut when he felt a shock of heat zip up his arm and through the nerves of his spine and making his head spin. His jaw tightened painfully as he felt his gut tighten and twist, his body tingled in pins and needles until everything stopped. His body felt cold. The cold you felt before you were about to pass out. Waiting and waiting but it never did. Everything felt weightless. Carefully he opened his eyes to see himself eye level with Bill, the demon practically beamed with excitement.

“Tada~!!!” the triangle clasped his hands together and moved behind him, pushing at his shoulders to get him to move with him. 

Dipper moved to walk but his footsteps were met with absolutely no resistance to the air he floated in. Wait, why was he floating? He allowed Bill to push at him as he tried to piece everything together, his mind fuzzy with it all until he was presented in front of the mirror in the room. Bill moved to his side and wrapped an arm around him. When Dipper looked up to see his reflection his eyes widened- well, rather eye. Instead of his normal, fleshy self he was used to seeing whenever he looked at himself he was presented with a form he had to roll his eyes at later when the initial shock of it all wore off. He was in a angular shape just like Bill, but rather being a triangle he was a simple silhouette of a two tiered pine tree, blue just to match his old worn hat he had been known to wear. He swatted Bill’s arm away from him so he could moved closer to the mirror, his own small hands pressing against the cool glass. He had no true features aside from the shape, his limbs which were now more noodle like than usual, and the one single eye. He looked over at Bill to speak but stopped himself. He didn’t even know if he could! Touching at his form to find a mouth in worry.

“Relax, you’ll get used to it! You’re overthinking it!” Bill cooed and floated over to him once more to wrap an arm around him to lead him along, “See, this is what I wanna try out. Show you what it’s all like from my side,” he poked at one of Dipper’s slopes, “You like new experiences, right?”

Dipper blinked, honestly he wasn’t entirely sure what to think about all of this but he went to answer. But all that came out was a stuttered hum. The demon watched as the pine tree looked down at the floor space and his dangling legs, pulling them closer in anxious fear as they were suspended easily in the air. Instead of saying anything demeaning to him and telling him to suck it up, that it was fine, Bill decided to pull him along to the edge of the bed. Dipper’s feet connected with the plush surface as he was returned to a more familiar way of moving around for him, being able to walk he watched every step as if he had never done so before. 

Bill on the other hand easily made his way to the head of the bed and patted at the pillow, clearing his throat to catch the other’s attention, “Up here, sapling.”

He blinked, stepping over to where the triangular one was at, finally he found his voice, “W-wait, a-re we-”

“Of course! Pine Tree, I told you that I wanted to try something new, and this is it!” Bill explained and carefully tugged at the other’s wrist to get him to settle into the once fluffier pillow, “If you don’t like it, we’ll never do it again! But we’ll never know unless we try, got it? Got it. Good.”

He didn’t say anything, shifting his weight back and forth on his hands. He wasn’t even sure how this was at all going to work. Neither had mouths, genitals, anything at all in forms like these. Bill narrowed his eye as he heard the other’s confused thoughts. Snapping his fingers a small tear appeared in the air behind Dipper.

“No mind to all that, Sapling, this is all where magic comes into play! And trust me, it feels pretty great. Think of this form as, another kind of sensory deprivation!”

Before he could find his voice again, Bill decided to press their ‘faces’ together in some sort of kiss. The action made Dipper relax a bit, his hand moving down to find one of Bill’s to entwine their small fingers together.

“I do-nt,” his voice was still small and faint, still trying to figure out how to speak in this form, “Know, wha-at to do…”

“That’s fine, relax, leave it all to me~,” Bill practically purred and knelt down in front of the other.

Dipper would’ve nodded, but instead he closed his eye and took in a deep breath. Putting his entire trust in the demon, whether that was a truly good idea or not he didn’t really think too much of it at the moment. Bill moved his unheld hand over to run the other’s side, from the top slope all the way down. Dipper took in a sharp breath at the simple sensation over his now extremely sensitive sides. His fingers tightened around Bill’s hand. The demon hummed and circled his thumb in one of the dips of the other’s side before Dipper jumped. His eye snapped open when he felt something slender slither down his back followed by a low hum from the other to comfort him, letting him know it was okay. 

When he felt two hands push at what he would assume to be his shoulders, just above his thin arms, Dipper allowed himself to be pushed back to sit on the pillow. His eye opening slightly to give a small quizzical gaze to the other. His gaze widened when he watched the way Bill’s form cracked above the dinky bowtie he wore. He was confused and he seemed to know this, which only made the visible line upturn into a smile before Bill bared his familiar teeth; sharp and jagged.

Bill beat him to it, “Didn’t know I had a mouth in this form, did’ja?”

“You never told me!” Dipper’s voice came out more defensive than what he actually was, he was more confused and taken back than anything at the moment.

“I don’t tell you things that aren’t relevant, kid,” Bill rolled his eye, “Besides, you never enjoy hanging out with me in my form like this for too long, it’s your own fault for the lack of knowledge.”

The younger scowled but before he could say anything Bill shushed him, kneeling to him and pressing actual kisses just below his eye. A small noise escaped Dipper as he leaned back on his hands, the tentacle behind him pressing into his back to prevent him from leaning too far back. He chose to close his eye rather than watch the way Bill peppered his tree silhouette form with kisses, edging closer and closer to his sides where his hands were loosely placed. The former brunette jumped when he felt an oddly warm tongue lap up one of his sides before pulling back, his hands balling the fabric at the sensitive action. He felt himself sink back further as much as the tendril would allow him to.

“Is, this what it feels like for you?” Dipper whispered as the demon went to work and licking his long tongue up his sides teasingly.

Bill hummed, moving to run his hands over the front and back of the other as his mouth worked at the sides, “Yeah. Didn’t think it felt this good, huh?”

“Nuh-uh…”

All that was heard was another hum from the golden. Dipper’s eye was contently closed, fingers curling and uncurling as he allowed himself to focus on his side. Another tentacle slipped through the small rift of Bill’s controlled mindscape, practically dripping with the slick sickeningly sweet fluid he had come to acquaint them with. Not like he would be tasting any of it though, not at this time. The tendril moved silently over to his vacant side more running the entire length of his side. The liquid made itself known instantly, familiarly warm and wet before catching the air and cooling to the point where normally Dipper would have goosebumps. He shuddered at the sensation of both Bill’s tongue and the tendril at his sides. Honestly, at this point he still wasn’t even sure if he had toes. But if he did they’d sure as hell be curling right now.

Bill trailed his fingertips up the younger’s front, carefully nipping with his teeth at the tiered sides he had for now. His fingers moved without any real destination, tiptoeing here, slipping over there, a few traces everywhere. When he added his nails into the mix it made Dipper both physically and verbally shudder, eye fluttering at the sensation of it. He felt like his entire body was stricken with pins and needles, but nothing painful nor uncomfortable like it. Feeling warm and fuzzy as if his entire body was on fire, which probably was his entire body seeing how much smaller he was right now. 

“Lean back, Sapling,” Bill’s voice came out in a rich whisper that earned an audible squeak.

The tendril once at his back moved to his front and gently nudged him to lay back before it draped itself loosely over his form and hooked slightly around him, as if to hug him. The slick tentacle pulled back from a moment much to the displeasure of Dipper, but he didn’t say anything nor did he move to pull it back. Instead he simply stared at the ceiling and waited for Bill to say or do something, he could feel him move around until he was below him. Bill sat on his heels and hummed to himself, running his finger tantalizingly slowly down the other’s side and down the length of his legs.

When Dipper moved to sit up the tentacle around him tightened slightly, “B-ill? What’re you doing? What are you gonna do?”

“Nothing we’ve never done before~.”

“I- We’ve never done ANY of this before, that doesn’t comfort me at all,” The dripping appendage moved closer to nudged his cheek as if to calm him someway, getting him to squeeze his eye shut at the action.

“Trust me, Kitten, nothing we’ve never done before,  _ before.” _

And with that Bill pushed at his Pine Tree’s legs and held them apart, bringing his tongue along the underside of him. Just with the way Bill’s own body was, well form when he was like this, Dipper’s underside had softened greatly from the normally hard surface it usually was, to an easily penetrable opening for him to slip his tongue into. Or anything else he wanted to for that matter. Instantly Dipper jerked at the feeling. Sure Bill rimmed him all the time, in his human form. But this was nothing like that. Well, okay that was an overstatement. But it certainly didn’t feel like normal. It felt as though that warm tongue was entirely inside of him, but he knew better than that. It felt as though it was wriggling up to his nonexistent stomach, between his lungs, twisting with his own. He didn’t know how to describe it, or what to focus on. He felt strangely full. At some point Bill was able to let go of his legs to hold at him and lift him to a better angle to push and pull his tongue inside of him, flicking the wet muscle in different directions to see which sigh or mewl he enjoyed more coming from his Sapling.

“B-ill, thi-s, this is we-ird,” Dipper’s voice came out as a huffed whisper, his fingers rooted into the fabric beneath them, white knuckling it but void of color, “So- ooohh, weird…”

Bill didn’t say anything. The slick tendril moved back to Dipper’s side, pressing firmly against him and working itself slowly at first in small circles downwards till the end of the first tier before it licked back and forth along it. The patches along his form below his eye had flushed a deep indigo by now. His eye lidded and glazed over with arousal as the tentacle worked at him and Bill thrusted his tongue in and out of him. The feeling that was washing over him that intensed with every passing second finally registered in his foggy mind.

His eye widened and moved to sit up again only to be pinned down, “Bill! No!”

“Hnnn?”

“I can’t! N-no, pl-ease, I do’dont-”

“ ‘ou ‘an tell me in a ‘e’c’nd,” Bill pressed on further knowing exactly what was going on.

Dipper emitted a loud whined that died into a huff as he settled back against the pillow tensed. He was gonna cum. Could he even cum in this form? He wasn’t sure, and he was in a sense afraid to find out. What if he couldn’t, what if it was like some sort of denial thing that his form couldn’t fully register it? Dipper was nervous and anxious. The tentacle pushed harder against him, leaking at his side, while Bill pushed his tongue against what he had come to guess his sweet spot was and sending pleasurable static through him. Dipper was mewling one after another as he brought ever so closer to that edge before-

“F-f-uck! B-iLLLL, Billbillbillbillbillllll, oh-h god,” Dipper’s form flushed a darker shade as he slapped a hand over where his mouth would be to shush himself. 

His awaiting orgasm hit him harder than normal, he wasn’t entirely sure the reason but he could assume because of the form he was in. Washing over him from his core in an intense warmth that fanned out through him all the way to the ends. The tip of Bill’s tongue continued to flick slightly inside of him and send small sparks through him, causing him to tense every time. It was a full body experience that was concentrated, or perhaps it was the old saying big things come from small packages- he wasn’t sure. All he knew is that it felt, actually pretty great.

The tentacle at his side pulled away slowly, leaving a trail of it’s own fluid connecting between it and Dipper. Bill followed suit, pulling his tongue out of the other before he sat up straight with a lick of his lips. Dipper laid against the pillow entirely spent, his eye shut in pure content. Bill watched and pulled the tentacle that was hooked around his Pine Tree, allowing it to slide across his form before pulling back and poking the mortal’s cheek. Dipper scrunched his eye up and batted it away with a hum of annoyance. Bill simply retracted both tendrils back into their rift before snapping his fingers to close it. Dipper didn’t flinch. 

The demon then crawled over the other’s form, a smile on his form as he kissed the still present indigo hue on his features, “You did so well, Pine Tree.”

“Hnnmm…”

“So well,” Bill whispered, kissing small kisses all the way up until kissing Dipper’s eyelid.

Dipper wiggled beneath him, eye still closed he moved to grab at Bill’s sides to pull him close. Lacking a mouth he’d make up for it later, but for now Dipper pressed their foreheads together and tiredly looked at him, “I love you, Bill.”

Bill blinked, causing the other to close his eye at the butterfly kiss, his own softened as he brought a hand up over one of his, “Love you too. You’re exhausted, Sapling, don’t worry you’ll be back to normal when you wake up. But for now, you’re welcome to sleep.”

“You sure?”

“Yeah.”

“Saaap,” Dipper hummed in playfulness before dropping his arms over his form, eye falling heavily closed.

“You’ll make it up to me later,” Bill crawled off of him with one last kiss, deciding to settle down next to him and watch as he drifted off. Paying close attention to his consciousness. 

* * *

Bill was right. When Dipper woke up the next morning, as naked as ever, he was excited to see that he was back in his normal human self. Smiling to himself he didn’t fully notice the other in bed with him until Bill hummed tiredly and sat up next to him, shirtless and in his human vessel.

“You seem happy,” Bill stretched his arms a bit from sleeping in the shared twin bed “Who knew you were a morning person.”

“Gross, no, I hate mornings. I just… Kinda missed my body, okay?”

The blonde looked at him with a bit of worry behind his pale blue eyes, trying to mask the emotion he cleared his throat and reached for the foot of the bed in a stretch, “You weren’t away for that long, geez. If you didn’t like it don’t nag me on it, we won’t do it again.”

“I didn’t say I didn’t like it,” Dipper’s voice came out a bit smaller than he had expected, toying with a dark curl, “It’s something i’m not used to… But, maybe if we fool around some more like that… I would be.”

Bill stopped his stretching, looking over his shoulder at the coyly smiling human, “Are you serious?” he got a small nod, “You-, you actually wanna do that again?”

“Yeah, I mean. You’re right. You always turn human for me, and i’ve never once thought about maybe doing something along the lines of it for you,” Dipper’s finger curled around the lock of hair before he locked eyes with Bill, “It’s something I liked, I got to experience things like you do.”

The two stared at each other for a moment, an expression on the older’s face that was taken back. He stared at Dipper unblinking like a cat before it made him uncomfortable, his smiling dropping a bit and shifting a bit, “Dipper, I love you.”

 

**Author's Note:**

> What the fuck
> 
> I DONT FUCKNIG WRITE FOR NEARLY A MONTH ANF THEN WHEN I DO THIS IS WHAT I DO JEsus fucking christ. Anyway i have another smut idea that involves, okay actually two ideas, that involve Shape!Dipper. Yeagh... Is BillDip still a thing? Is Gravity Falls still relevant? Is it still a thing? I don't know.
> 
> If you haven't heard, my laptop died. Officially. Boom. Dead. Wanna know how i wrote this? I hooked up a desktop laptop to my tablet. That is literally my fucking set up right now. So it's taking me a bit to get used to it but i think i've nailed it a bit..
> 
> Anyway, point out spelling errors and grammar, oh you know the drill
> 
> C/K/B/Etc~!


End file.
